"we are dealing with a person (the MLCer) who displays many of the traits of a full blown sociopath."

Yes, this is it... I'd not been able to formulate quite what it was that I found so disturbing about not receiving understanding/validation from others.

But this is the nub of the issue. And no-one, aside from those who've been through it themselves, seems to understand.

It's not just "oh well, you two have split up. Move on; get over it"

Peace's SIL seems to understand that it was something much more than this.